Very little is known about the interface chemistry of ternary semiconductor alloys. The data available on compound semiconductors can be extrapolated only in part to ternary alloys, where the interplay of two different kinds of chemical bonding can substantially change the character and stability of each bond with respect to those of the binary parent compounds. Hg.sub.1-x Cd.sub.x Te ("MCT") is probably the ternary semiconductor most studied in recent years because of its widespread application for infrared detectors in the 8-14 .mu.m spectral range. See P. W. Kruse, "Optical and Infrared Detectors," in Topics in Appl. Physics, R. J. Keyes, et., Vol. 19, Springer-Verlag, New York, NY (1980), at page 7.
This material poses a number of intriguing fundamental and technological problems that only now are starting to be addressed. As a ternary semiconductor alloy formed from parent compounds of very different stability, this material easily undergoes composition variations. It has also been recently recognized that the interplay of ionicity and metallicity in the two kinds of chemical bonding that coexist in the matrix further weakens one bond (Hg-Te) relative to the other (Cd-Te), causing lattice, surface and interface instabilities in the alloy. For example, dramatic composition variations have been observed in Hg.sub.1-x Cd.sub.x Te as a result of processes as diverse as mechanical damage, oxidation and metal deposition.
Simple metals such as aluminum and indium react with MCT to form tellurides, induce a severe mercury (Hg) depletion in the near-surface region and/or atomic interdiffusion into the semiconductor. The consequences can include unreproducible metallization parameters and reduced contact stability and reliability.
Therefore, there is a need for a method to fabricate reliable metal contacts on MCT semiconductor surfaces.